1. Field of the Invention
This invention relates generally to implantable devices for interventional therapeutic treatment or vascular surgery, and concerns a stranded micro-cable with enhanced radiopacity that can be used to fabricate a vascular device, a stent, a guidewire or the like. More particularly, the invention relates to three dimensional microcoil vasoocclusive devices fabricated from stranded micro-cable.
2. Description of Related Art
The art and science of interventional therapy and surgery has continually progressed towards treatment of internal defects and diseases by use of ever smaller incisions or access through the vasculature or body openings, in order to reduce the trauma to tissue surrounding the treatment site. One important aspect of such treatments involves the use of catheters to place therapeutic devices at a treatment site by access through the vasculature. Examples of such procedures include transluminal angioplasty, placement of stents to reinforce the walls of a blood vessel or the like and the use of vasoocclusive devices to treat defects in the vasculature. There is a constant drive by those practicing in the art to develop new and more capable systems for such applications. When coupled with developments in biological treatment capabilities, there is an expanding need for technologies that enhance the performance of interventional therapeutic devices and systems.
One specific field of interventional therapy that has been able to advantageously use recent developments in technology is the treatment of neurovascular defects. More specifically, as smaller and more capable structures and materials have been developed, treatment of vascular defects in the human brain which were previously untreatable or represented unacceptable risks via conventional surgery have become amenable to treatment. One type of non-surgical therapy that has become advantageous for the treatment of defects in the neurovasculature has been the placement by way of a catheter of vasoocclusive devices in a damaged portion of a vein or artery.
Vasoocclusion devices are therapeutic devices that are placed within the vasculature of the human body, typically via a catheter, either to block the flow of blood through a vessel making up that portion of the vasculature through the formation of an embolus or to form such an embolus within an aneurysm stemming from the vessel. The vasoocclusive devices can take a variety of configurations, and are generally formed of one or more elements that are larger in the deployed configuration than when they are within the delivery catheter prior to placement. One widely used vasoocclusive device is a helical wire coil having a deployed configuration which may be dimensioned to engage the walls of the vessels. One anatomically shaped vasoocclusive device that forms itself into a shape of an anatomical cavity such as an aneurysm and is made of a pre-formed strand of flexible material that can be a nickel-titanium alloy is known from U.S. Pat. No. 5,645,558, which is specifically incorporated by reference herein. That vasoocclusive device comprises one or more vasoocclusive members wound to form a generally spherical or ovoid shape in a relaxed state. The vasoocclusive members can be a helically wound coil or a co-woven braid formed of a biocompatible material, and the device is sized and shaped to fit within a vascular cavity or vesicle, such as for treatment of an aneurysm or fistula. The vasoocclusive member can be first helically wound or braided in a generally linear fashion, and is then wound around an appropriately shaped mandrel or form, and heat treated to retain the shape after removal from the heating form. Radiopacity can be provided in the vasoocclusive members by weaving in synthetic or natural fibers filled with powdered radiopaque material, such as powdered tantalum, powdered tungsten, powdered bismuth oxide or powdered barium sulfate, which can potentially be released during vascular surgery.
Another occlusion device for closing defects in vascular walls is known that is formed by a pair of distinct sections of varying configuration, which may be parabolic or conical bodies oriented to flare outward. Yet another implantable vasoocclusive device is known that is formed by a complex, helically wound coil adapted to take on a secondary shape suitable for snugly fitting within a given vascular cavity upon deployment, that can be formed by winding the coil on a mandrel having radially extending poles.
The delivery of such vasoocclusive devices can be accomplished by a variety of means, including via a catheter in which the device is pushed through the catheter by a pusher to deploy the device. The vasoocclusive devices, which can have a primary shape of a coil of wire that is then formed into a more complex secondary shape, can be produced in such a way that they will pass through the lumen of a catheter in a linear shape and take on a complex shape as originally formed after being deployed into the area of interest, such as an aneurysm. A variety of detachment mechanisms to release the device from a pusher have been developed and are known in the art.
For treatment of areas of the small diameter vasculature such as a small artery or vein in the brain, for example, and for treatment of aneurysms and the like, micro-coils formed of very small diameter wire are used in order to restrict, reinforce, or to occlude such small diameter areas of the vasculature. A variety of materials have been suggested for use in such micro-coils, including nickel-titanium alloys, copper, stainless steel, platinum, tungsten, various plastics or the like, each of which offers certain benefits in various applications. Nickel-titanium alloys are particularly advantageous for the fabrication of such micro coils, in that they can have super-elastic or shape memory properties, and thus can be manufactured to easily fit into a linear portion of a catheter, but attain their originally formed, more complex shape when deployed. Although various materials are more or less kink resistant when nickel-titanium alloys are dimensioned into wire smaller than approximately 0.010 inches in diameter, they can have low yield strength and can kink more easily, thus severely limiting the applications for such finely drawn wire in the fabrication of vasoocclusive devices. As a further limitation to such applications, nickel-titanium alloys are also not radiopaque in small diameters, and a single nickel-titanium wire would need to be approximately 0.012 inches in diameter to be even slightly radiopaque. However, such a thickness of a single nickel-titanium wire would unfortunately also be relatively stiff and possibly traumatic to the placement site, particularly if used for treatment of delicate and already damaged areas of the small diameter vasculature such as an aneurysm in an artery or vein in the brain, for example.
One conventional guidewire for use in a catheter is known that is made of a high elasticity nickel-titanium alloy, and is useful for accessing peripheral or soft tissue targets. The distal tip of the guidewire is provided with a radiopaque flexible coil tip, and a radiopaque end cap is attached to the guidewire by a radiopaque ribbon. Such a construction is complex to manufacture, fragile and can potentially break off during use with undesirable results. A stretch resistant vasoocclusive coil is also known that can be made of a primary helically wound coil of platinum wire, with a stretch-resisting wire attached within the primary coil between two end caps. Unfortunately, such a construction is relatively difficult to fabricate and also fragile, allowing for the possibility of the fracture of the central radiopaque wire, the coil, the welds or some combination of them, and it can also potentially break off during use. Also, such a construction has a complex and nonlinear bending characteristic, dependent on the spacing of the coils and central wire and the radius of the bend of the coil.
From the above, it can be seen that vasoocclusive devices and their attendant deployment systems provide important improvements in the treatment of damaged neurovascular areas. However, there remain important limitations in the technology presently available to fabricate these devices. It would therefore be desirable to provide a structural element that can be incorporated into a stent, guidewire, micro-coil or the like, which offers the advantages of a shape memory alloy such as a nickel-titanium alloy, and that incorporates radiopaque material in a stable configuration that is not subject to breaking during use of the device, so that the device can be visualized under fluoroscopy. It would also be desirable to be able to create a variety of three dimensional vasoocclusive shapes that can be deployed from a catheter into an aneurysm or other defect and to thereby provide an efficient therapy for treatment of the defect. The present invention meets these and other needs.
Significant advances have been made in the treatment of neurovascular defects without resolution to surgery. More specifically, micro catheters have been developed which allow the placement of vasoocclusive devices in an area of the vasculature which has been damaged. In presently used techniques, the vasoocclusive devices take the form of spiral wound wires that can take more complex three dimensional shapes as they are inserted into the area to be treated. By using materials that are highly flexible, or even super-elastic and relatively small in diameter, the wires can be installed in a micro-catheter in a relatively linear configuration and assume a more complex shape as it is forced from the distal end of the catheter.
In order to gain the advantages presently being realized with micro-catheter therapies and procedures to repair damage to the vasculature in the brain and other vessels, shape memory materials such as nickel-titanium alloys have been incorporated in vasoocclusive devices to be placed by the catheters. However, the range of diameters of wire and the configurations of the resulting geometry of both the coils and the devices developed which can be used have been limited by both the relatively small diameter of wire that must be used to avoid trauma and allow housing within the catheter prior to deployment, and the requirement for larger diameters to provide for radiopaque markers and mechanical robustness. In many cases this has resulted in primary wire characteristics in the coil that are unacceptably stiff, very delicate, or subject to kinking. The present invention obtains significant advantages over such prior art devices by providing a cable of multiple strands of an alloy adapted to be used in catheters, stents, vasoocclusive devices, guidewires and the like, thus providing a kink resistant, high strength material with highly desirable performance characteristics which can be altered by construction details to suit a variety of interventional therapeutic procedures.
More specifically, it has been found that single strands of small diameter nickel-titanium alloys, as well as other metal alloys, used to form vasoocclusive devices can be kinked if twisted and pulled as can occur during or after deployment from a catheter, especially if the doctor wishes to withdraw a partially deployed coil because it is somehow incorrect in size, shape or length to repair the damage to the vessel. Also, single wire coils are more likely to cause trauma to the area to be treated if the wire is of a sufficient diameter to provide adequate tensile strength. Furthermore, such small diameter wires of some of these materials such as nickel-titanium, stainless steel and the like, are not generally radiopaque with currently available equipment, necessitating the use of radiopaque markers attached to the device, with the resultant possible diminution of functionality and increased diameter.
The present invention solves these and other problems by providing, in its broadest aspect, a micro-cable which includes at least one radiopaque strand to offer a continuous indication under fluoroscopy of the deployed configuration of the device incorporating the micro-cable. When combined with the benefits of a material such as nickel-titanium in the other strands of the micro-cable, numerous advantages are available from the use of this basic construction in interventional medicine.
Briefly, and in general terms, a presently preferred embodiment of the present invention provides for a multi-stranded micro-cable made of a suitable material such as stainless steel or a nickel-titanium alloy, with the cable including at least one radiopaque strand, made of platinum, tungsten or gold, in order to serve as a marker during a procedure. The multi-stranded micro-cable can be configured into a stent, guidewire, micro-coil or the like used in micro-catheters, for example, to restrict, reinforce, or to occlude areas of the small diameter vasculature such as an artery or vein in the brain, for example, for treatment of aneurysms and the like.
In one presently preferred embodiment, the invention accordingly provides for a multi-stranded micro-cable formed of a plurality of flexible strands of a super elastic material, and at least one radiopaque strand. In one presently preferred embodiment, the multi-stranded micro-cable comprises a plurality of flexible strands of nickel-titanium alloy, the micro-cable having at least one central axially disposed radiopaque wire, such as platinum, tungsten or gold, for example, in order to provide a radiopaque marker during vascular procedures. In this preferred embodiment, the construction of the invention places the lowest tensile strength and highest flexibility member, the radiopaque marker strand, in a position in the cable which results in minimum stress on that member; at the same time, the super elastic material is in the outer strands, which have the dominant affect on performance parameters, thus enhancing the benefits of the material. Another benefit associated with the invention compared to prior art devices is that the multiple stranded cable configuration, in addition to providing a highly flexible and resilient structure, eliminates the necessity of a safety wire, since the failure of a single strand will not cause a severing of the cable. Also, the construction prevents stretching of the cable in the event of failure of a single strand, which is a significant benefit compared to constructions which have a coil around a central safety wire.
In a second presently preferred embodiment, the invention includes a multi stranded cable constructed of multiple twisted strands of a suitable material such as a shape memory alloy or super elastic alloy of nickel-titanium, with one or more of the twisted strands consisting of a radiopaque material. The radiopaque strand may be one or more of the peripheral twisted strands and may also include one or more central strands of the cable. In a preferred aspect of the embodiment, the cable consists of six peripheral twisted strands and a central linear core strand, one or more of which can be of radiopaque material.
In a third aspect of the invention, the cable can be of linear strands that are arranged in a bundle and fastened or bound at intervals, or continuously, in order to maintain contact among the strands as the cable is bent. One or more of the strands may be radiopaque. This construction is adaptable to guidewires and other structures that must be pushable and/or torqueable, but still remain highly flexible and include radiopacity. Variations on this embodiment can include an outer sheath which consists of a solid or helically wound cover to provide enhanced torqueability and pushability. More specifically, the outer sheath can vary in thickness, stiffness of material or spring of the sheath members to provide desired variations in bending or stiffness of the cable. Such a construction is particularly adaptable to guidewires and the like, and can be varied in terms of the binding or outer layer to alter the torqueability of the cable, and the flexibility of the cable can be varied along its length by the number and sizes of the stranded members in the cable.
In a fourth aspect of the invention, one or more of the strands can be of a therapeutic material used to enhance treatment of the site after placement of the device. In one presently preferred embodiment of the invention, the cable includes twisted strands of wire around the periphery of the cable, at least one of which is radiopaque. The core of the cable contains a therapeutic agent such as human growth hormone, genetic material, antigens or the like that are intended to become active after placement. Such a construction can be adapted to a variety of interventional therapeutic treatments. In one aspect of this embodiment, one of the strands can have multiple functions, such as providing both a therapeutic effect and also contributing to the structural integrity of the cable. By using copper in such a micro-cable, for instance, the copper can enhance the use of a device made from the cable as an intrauterine device, with the copper also contributing to the radiopacity and structural integrity of the micro-cable. In the event that such an effect is desired, the therapeutic strand can be placed on the exterior of the cable to enhance contact with the site to be treated.
In a fifth aspect of the invention, a three dimensional occlusive device is provided that is adapted to be inserted into a portion of a vasculature for occluding the portion of the vasculature for use in interventional therapy and vascular surgery, that comprises at least one multi-stranded micro-cable having a plurality of flexible strands of a resilient material, with at least one radiopaque strand to provide a radiopaque marker of the deployed configuration of a device made of the cable during vascular surgery. The occlusive device is configured to have a primary, collapsed coil configuration or shape, and an expanded, or secondary three dimensional coil configuration or shape, that can be generally helical, conical, or spherical shapes. The flexible strands in a multi-stranded micro-cable of the occlusive device can be helically wound, or can be configured as parallel, longitudinal strands. In a currently preferred embodiment, at least one of the strands comprises a super-elastic material. In another currently preferred embodiment, a plurality of the strands comprises a super-elastic material. One presently preferred super-elastic material comprises a nickel titanium alloy, that can be heat treated such that the alloy is highly flexible at a temperature appropriate for introduction into the body via a catheter, and after placement, the device will seek its minimum energy shape as originally formed and thereby take on a shape designed to optimize the therapeutic purposes desired for the device.
In another aspect of the invention, at least one of the strands comprises a shape memory material. In another currently preferred embodiment, a plurality of the strands are comprised of a shape memory material. One presently preferred shape memory material comprises a shape memory polymer. In one configuration, the strands of the micro-cable are arranged as exterior strands surrounding at least one interior strand, or core, and at least one radiopaque strand is disposed in the micro-cable, either centrally, axially disposed in the bundle of strands, or in the exterior strands surrounding the central core. The micro-cable can include a plurality of radiopaque strands, such as platinum, gold, or tungsten.
In the fifth aspect of the invention, at least one of the strands in the core or exterior strands can comprise a therapeutic agent, such as a copper or copper alloy wire or any of a variety of therapeutically active metals, alloys or components, a fiber such as Dacron (polyester), polyglycolic acid, polylactic acid, fluoropolymers, nylon, polyaramid fiber (e.g.Kevlar(copyright)), or silk chosen for thrombogenicity. Since the micro-cable consists of stranded parts, one or more strands may be longer than others, or even intermittently terminated, to thereby extend beyond the diameter of the remaining strands and thereby increase the therapeutic effect of that strand. Alternatively, at least one of the strands can be coated with or impregnated with a therapeutic material, which can include, but is not limited to, any one or combination of human growth hormone, genetic material, antigens, hydrogels, collagen, bioabsorbable polymers such as lactic acids/glycolic acids, caprolactam or microcellular foam. In addition, the therapeutic element can comprise a means to conduct energy, such as an optical fiber to conduct light energy.
In the fifth aspect of the invention, the strands of the micro-cable can also be bundled by at least one outer cover or sheath to constrain the strands of the micro-cable about a longitudinal axis to produce a composite banded cable. The outer sheath can comprise a containment strand wound about the strands and made of a low friction material, such as a fluoropolymer, for example, or a heat shrinkable plastic tube. In one feature of the fifth aspect of the invention, a plurality of heat shrink plastic covers are placed over the strands of the micro-cable to provide bending stiffness in the cable. The strands of the micro-cable can be banded at intervals by a plurality of bands. In another variation, a plurality of micro-cables that are arranged as parallel, longitudinal micro-cables or a helically wound micro-cables to form a composite cable can have an exterior wrapped cover that can be wound at greater or lesser intervals along the outside to provide variations in the torqueability and stiffness of the composite cable. Also, the thickness and width of the wrapping cover, as well as its material composition along the composite cable can vary in cross section along the length of the composite cable to provide bending stiffness of said cable which varies with the position on said cable. Also, the number of strands and the degree to which they extend along the composite cable can be varied within the sheath, and the outer sheath itself can be multi-layered with different materials in order to provide a graduated bending and stiffness characteristic over the length of the cable. The occlusive device thus can be formed of a plurality of micro-cables in order to provide desired bending and strength characteristics, either as helically wound micro-cables, or parallel longitudinal micro-cables having a collapsed composite cable configuration and an expanded composite cable configuration with a secondary shape. In another feature of the fifth aspect of the invention, the composite cable can further comprise at least one longitudinal sensing element for sensing a parameter, such as an optical imaging element, i.e., where the sensing element can comprises an optical fiber. Alternatively, the sensing element can comprise a thermal imaging element, or an ultrasound imaging element, for example.
In a further aspect of the invention, the form about which the three dimensional shape is wound is formed from metal, ceramic or other heat resistant material and has formed within it the path desired for the micro-cable corresponding to the shape. For example, the form can be of a spherical configuration, with the surface containing channels into which the cable is laid prior to heat treating. The channels can be arranged so that the resultant shape is kink resistant and relatively easy to withdraw without kinking. The form can also contain passages through which the cable can pass to advantageously form the shape.
After the cable is wound around the form, the form and cable can be heat treated to cause the cable material to adopt the shape of the form as a low energy shape. The cable can then be removed from the form and put into a catheter-introducer prior to use in intravascular therapy.
In another presently preferred embodiment, the invention comprises a device for use in interventional therapy and vascular surgery, adapted to be inserted into a portion of a vasculature, comprising a shape memory coil having an outer coil portion and an inner core portion, the shape memory coil having a collapsed primary coil configuration and an expanded secondary configuration with a three dimensional shape; and a radiopaque strand extending through the core of the shape memory coil to provide a radiopaque marker of the deployed configuration of the device. In one presently preferred embodiment, the shape memory coil comprises a multi-stranded coil having a plurality of flexible strands of a resilient material, and in an alternate preferred embodiment, the shape memory coil comprises a single stranded coil, such as of a nickel titanium alloy, or a shape memory polymer, for example. The radiopaque strand enhances the radiopacity of a multi-stranded coil, as well as a single stranded coil of pure nickel titanium alloy, which will advantageously not fray upon stretching, and is stretch resistant. With such an inner radiopaque strand, the coil can also be made of other materials, such as a shape memory polymer such as polyurethane, for example.
In a presently preferred embodiment, the radiopaque strand comprises a core strand having a plurality of intermittently spaced apart enlarged radiopaque portions that can comprise a radiopaque material selected from the group consisting of platinum and gold, for example. The core strand can comprise a material selected from the group consisting of platinum, gold, a shape memory polymer having a glass transition temperature (Tg) below 25xc2x0 C., a hydrogel, an amorphous gel, and a fiber. In one presently preferred aspect, the enlarged radiopaque portions can comprise a plurality of beads of radiopaque material spaced apart and mounted on a core strand of material, and the beads may comprise a radiopaque material selected from the group consisting of platinum, gold and tungsten. In another presently preferred aspect, one or more of the plurality of beads can optionally be bonded to a segment of the shape memory coil, such as an end bead bonded to an end segment of the shape memory coil, for example.
In another presently preferred aspect, the enlarged radiopaque portions may comprise a plurality of coils intermittently wound about and spaced apart on the core strand, and the core strand can comprise a radiopaque material selected from the group consisting of platinum and gold. The spaced apart coils can comprise a radiopaque material selected from the group consisting of platinum and gold.
In another presently preferred embodiment, a polyhedral occlusive device is provided, adapted to be inserted into a portion of a vasculature for occluding a portion of the vasculature, for use in interventional therapy and vascular surgery. The occlusive device can be formed with multiple coils centrally connected together at their inner ends to a central coil body and radiating outward from the central coil body. When inserted within a vessel at a treatment site, such as within an aneurysm, the radiating coil arms of the occlusive device extend to fill the vessel in three dimensions, allowing the occlusive device to accommodate the shape of the vessel.
In another presently preferred embodiment, the device for use in interventional therapy and vascular surgery includes a micro-cable or coil formed of one or more flexible strands of a resilient material, having a collapsed primary coil configuration and an expanded secondary configuration with a three dimensional shape; and one or more therapeutic fibers woven into the coil to enhance treatment of the site after placement of the device. The coil can also be formed to include one or more radiopaque strands to provide a radiopaque marker of the deployed configuration of the device. The one or more therapeutic fibers can be woven about adjacent or non-adjacent loops of the coil, or can be woven through multiple strands of adjacent loops of the coil. The one or more therapeutic fibers are made of a material that will provide a timed release of a therapeutic agent intended to become active after placement of the device, such as human growth hormone, collagen, a modified polymer with growth factor, genetic material for gene therapy, antigens, or the like. A plurality of therapeutic fibers can be provided so that the different fibers in the coil can provide different therapeutic agents to provide a range of therapies.